1. Field of the Invention
The present invention relates to improvements in a unit for supplying wafers to an ion implantation process unit and collecting the processed wafers therefrom for use in ion implantation end stations.
2. Description of the Prior Art
Conventional end stations for ion implantation apparatus generally comprise a unit for supplying unprocessed wafers onto a disk and a unit disposed adjacent the supply unit for collecting ion-implanted wafers from the disk as disclosed in Unexamined Japanese Patent Publication No. SHO 58-214260. This arrangement is disadvantageous because of the following reason: the number of wafers (10 to 30) accommodated in a cassette set in the wafer supply unit is generally larger than the number of wafers (5 to 20) that may be set in a disk, thus difficulties are encountered in (a) wafer transport means mechanism in collecting processed wafers in the cassette wherein the unprocessed wafers remain, (b) further supplying unprocessed wafers to the disk, and (c) finally, collecting all the processed wafers and returning them to the original supply cassette. However, for the identification of wafers, the production line including an ion implantation apparatus must specify the wafers to be accommodated in a specified cassette at all times. This has become an important problem in recent years, since a wide variety of wafers are produced in smaller quantities. Therefore, when required, the processed wafers in the cassette in the collection unit are usually placed into an empty cassette in the supply unit and then fed in to the production line, thereby requiring much labor and results in higher production costs.